It is known for a nozzle in hot runner injection molding apparatus to include a thermally conductive body and a thermally conductive tip. Furthermore, it is known for the nozzle to include a separate piece that joins to the nozzle body and retains the tip in place in the nozzle body. The tip surrounding piece is also typically used to form a seal surrounding the space between the nozzle and the mold component to which the nozzle transfers melt. Because the mold component is usually maintained at a different temperature than the tip at least for a portion of an injection molding cycle, the tip surrounding piece is typically made from a material that is less thermally conductive than the tip itself.
An example of such a nozzle construction is shown in U.S. Pat. No. 5,299,928 (Gellert). A problem with such nozzle constructions, however, is that the tip surrounding piece, which has a lower thermally conductive material than the tip, can impede heat transfer from a heater on the nozzle, to melt that is in the tip.
Thus, a need exists for new nozzle and molding apparatus constructions that have improved heat transfer efficiency.